This invention relates generally to a fusing apparatus employed in an electrophotographic printing machine, and more particularly concerns preventing wrinkling of the sheet of support material as it passes through the fusing apparatus.
In a typical electrophotographic printing machine, a photoconductive surface is charged to a substantially uniform level. Thereafter, the charged portion of the photoconductive surface is exposed to a light image of an original document. The irradiated area of the photoconductive surface is selectively discharged recording an electrostatic latent image thereon. The electrostatic latent image corresponds to the informational areas contained in the original document. Heat settable particles are attracted to the electrostatic latent image during development forming a powder image corresponding thereto on the photoconductive surface. A sheet of support material is then positioned closely adjacent to the powder image and the particles are transferred from the photoconductive surface thereto in image configuration. The particles are then permanently affixed to the sheet of support material forming a copy of the original document thereon. In general, all types of electrostatographic printing, which include both electrophotographic and electrographic printing, utilizes some form of fusing particles to the sheet of support material. However, in the present application, an electrophotographic printing machine will be described as exemplary of the class of electrostatographic printing machines employing such an apparatus.
Various techniques have been developed for applying heat to the particles on the sheet of support material. One approach is to pass the sheet of support material with the powder image thereon through a pair of opposed rollers. In a system of this type, a heated fuser roll and a non-heated backup roll are employed. Preferably, the heated fuser roll has the outer surface thereof covered with a polytetrafluoroethylene coating, sold under the trademark Teflon, to which a release agent, such as silicone oil is applied. An alternate approach has been to utilize a bare metal heated roll which has a low molecular weight polyethylene applied thereto as a release agent.
Hereinbefore, various techniques have been devised to advance the sheet of support material into the nip between the heated fuser roll and backup roll without the resultant fused copy having wrinkles therein. One technique heretofore utilized to prevent wrinkling has been to taper the ends of the fuser roll. However, this poses some difficulties in the manufacture of the rolls.
Accordingly, it is a primary object of the present invention to improve the fusing apparatus by minimizing wrinkles in the sheet of support material as it passes therethrough.